Civil Engineering Reference
In-Depth Information
Figure 29.
Typical dynamic TG curve of 2.5 g of plaster in air. Heating rate = 5°C min
-1
.
[23]
A typical calculation utilizing a TG trace (dynamic method) can be
described as follows. The mass losses in steps 1 and 2 are designated ML1
and ML2, respectively. Further,
H
is the mass of the hemihydrate in the
sample,
D
is the mass of dihydrate in the sample, and
I
is the mass of the
impurities in the sample. The values of
H
,
D,
and
I
can be calculated by the
following equations:
Eq. (10)
D
= ML1/0.1571
I
Eq. (11)
H
= (ML2 - 0.062
D
)/0.062
Eq. (12)
I
= 100 - (
D
+
H
)
The isothermal TG method is described as follows: The dihydrate and
hemihydrate are decomposed simultaneously during isothermal tests when
the temperature of the experiments is maintained at 250°C or higher. The
isothermal TG curves show the cumulative mass loss of these reactions
(Fig. 30). Two different analyses are required, one for the original sample
